Steering wheel control apparatus

ABSTRACT

A steering wheel control apparatus for controlling driving of a steering wheel of a vehicle includes a steering wheel drive section that drives the steering wheel in accordance with a target value, a shock probability determination section that determines whether the steering wheel may apply a physical shock to a vehicle driver, and a steering wheel driving restriction section that restricts driving of the steering wheel by the steering wheel drive section to reduce the shock applied to the vehicle driver when the shock probability determination section determines that the steering wheel may apply the shock to the vehicle driver.

This application claims priority to Japanese Patent Application No.2015-144035 filed on Jul. 21, 2015, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a steering wheel control apparatus forcontrolling driving of a steering wheel of a vehicle.

2. Description of Related Art

There is known a steering wheel control apparatus that controls drivingof a steering wheel of a vehicle regardless of a steering operation by avehicle driver to avoid a collision with an obstacle present ahead ofthe vehicle. For example, refer to Japanese Patent Application Laid-openNo. 2011-162004.

However, this steering wheel control apparatus has a problem in that thevehicle driver touching the steering wheel of the vehicle receives alarge physical shock if the steering wheel is driven to be turnedgreatly.

SUMMARY

An exemplary embodiment provides a steering wheel control apparatus forcontrolling driving of a steering wheel of a vehicle, including:

a steering wheel drive section that drives the steering wheel inaccordance with a target value;

a shock probability determination section that determines whether thesteering wheel may apply a shock to a vehicle driver; and

a steering wheel driving restriction section that restricts driving ofthe steering wheel by the steering wheel drive section to reduce theshock applied to the vehicle driver when the shock probabilitydetermination section determines that the steering wheel may apply theshock to the vehicle driver.

According to the exemplary embodiment, there is provided a steeringwheel control apparatus which enables driving a steering wheel safelyfor a vehicle driver.

Other advantages and features of the invention will become apparent fromthe following description including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram schematically showing the overall structure of anelectric steering system of a first embodiment of the invention;

FIG. 2 is a block diagram showing the structurer of an EPS-ECU (ElectricPower assisted Steering-ECU) included in the electric steering system;

FIG. 3 is a diagram showing a model of the steering mechanism of theelectric steering system;

FIG. 4 is a block diagram showing the entire control system of theelectric steering system;

FIG. 5 is a graph showing an advantage provided by the first embodiment;

FIGS. 6A and 6B are picture diagrams for giving a warning to a vehicledriver in the electric steering system of the first embodiment;

FIG. 7 is a block diagram showing the structure of a target trackingcontrol arithmetic section included in the electric steering system ofthe second embodiment of the invention;

FIGS. 8A and 8B are graphs showing advantages provided by the secondembodiment;

FIG. 9 is a block diagram showing the structure of a first modificationof the target tracking control arithmetic section included in theelectric steering system of the first or second embodiment of theinvention;

FIGS. 10A and 10B are graphs showing advantages of the firstmodification of the target tracking control arithmetic section;

FIG. 11 is a block diagram showing the structure of a secondmodification of the target tracking control arithmetic section;

FIG. 12 is a block diagram showing the structure of a third modificationof the target tracking control arithmetic section;

FIG. 13 is a graph showing an advantage of the third modification of thetarget tracking control arithmetic section;

FIG. 14 is a diagram showing a model of the steering mechanism in afirst modification of a vibration suppression control arithmetic sectionincluded in the electric steering system of the first or secondembodiment of the invention;

FIG. 15 is a block diagram showing the entire control system of thefirst modification of the vibration suppression control arithmeticsection;

FIG. 16 is a graph showing an advantage of the first modification of thevibration suppression control arithmetic section;

FIG. 17 is a block diagram showing the entire control system of a secondmodification of the vibration suppression control arithmetic section;

FIG. 18 is a graph showing an advantage of the second modification ofthe vibration suppression control arithmetic section;

FIG. 19 is a block diagram showing the entire control system of a thirdmodification of the vibration suppression control arithmetic section;

FIG. 20 is a graph showing an advantage of the third modification of thevibration suppression control arithmetic section;

FIG. 21 is a block diagram showing the entire control system of a fourthmodification of the vibration suppression control arithmetic section;

FIG. 22 is a graph showing an advantage of the fourth modification ofthe vibration suppression control arithmetic section;

FIG. 23 is a diagram schematically showing the overall structure of amodification of the electric steering system of the first or secondembodiment of the invention;

FIGS. 24A and 24B are diagrams showing a first example of a picturediagram for giving a warning to the vehicle driver in the modificationof the electric steering system;

FIGS. 25A and 25B are diagrams showing a second example of a picturediagram for giving a warning to the vehicle driver in the modificationof the electric steering system; and

FIG. 26 is a block diagram showing the structure of the modification ofthe electrical steering system provided with an variable gear ratiosteering actuator.

PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is a diagram schematically showing the overall structure of anelectric steering system 1 of a first embodiment of the invention.

As shown in FIG. 1, the electric steering system 1 includes a steeringwheel 2, a steering shaft 3, a torque sensor 4, an intermediate shaft 5,a motor 6, a steering gear box 7, tie rods 8, knuckle arms 9, and tires10. The electric steering system 1 also includes an EPS-ECU (ElectricalPower Steering ECU) 15 and a travel direction determination section 16.

Further, as shown in FIG. 2, the electric steering system 1 includes asteering wheel-holding state determination section 13, a brake ECU 18and a notification section 19. The steering wheel 2 is fixed to a firstend of the steering shaft 3 whose second end is connected with a firstend of the torque sensor 4. The torque sensor 4 is connected with theintermediate shaft 5 at its second end. In the following, the whole ofthe shaft body extending from the steering shaft 3 to the intermediateshaft 5 through the torque sensor 4 may be referred to as the steeringshaft.

The torque sensor 4 is for detecting a steering torque Ts. The torquesensor 4 includes a torsion bar which connects the steering shaft 5 andthe intermediate shaft 5 to each other to detect the torque applied tothe torsion bar as the steering torque Ts based on the torsion angle ofthe torsion bar.

The motor 6 is for generating an assist torque in accordance with assistcontrol and generating an automatic steering torque in accordance withtarget tracking control. The rotation of the shaft of the motor 6 istransmitted to the intermediate shaft 5 through a reduction gear device6 a. The reduction gear device 6 a includes a worm gear disposed at thefront end of the shaft of the motor 6 and a worm wheel disposedcoaxially with the intermediate shaft 6 in a state of being engaged withthe worm gear.

The rotation of the motor 6 is transmitted to the intermediate shaft 5.On the other hand, when the intermediate shaft 5 is rotated due to anoperation of the steering wheel 2 or a reaction force from the roadsurface (road surface reaction force), this rotation is transmitted tothe shaft of the motor 6 through the reduction gear device 6 a causingthe motor 6 to rotate.

In this embodiment, the motor 6 is a brushless motor provided with arotation sensor such as a resolver. The rotation sensor outputs a motorstate signal including at least a motor rotation angle θ, a motorrotation angular velocity ω and a motor rotation angular acceleration α.Alternatively, instead of the motor state signal, there may be used asteering angle, a steering angular velocity and a steering angularacceleration which can be obtained by multiplying the motor rotationangle θ, the motor rotation angular velocity ω and the motor rotationangular acceleration α with the gear ratio of the reduction gear device6 a. Further, a tire steering angle showing the steering angle of thetire relative to a reference angle (relative to the front direction ofthe vehicle, for example), a tire steering angular velocity and a tiresteering angular acceleration may be used instead of the motor statesignal.

The intermediate shaft 5 is connected to the torque sensor 4 at itsfirst end, and connected to a steering gear box 7 at its second end. Thesteering gear box 7 includes a gear mechanism constituted of a rack anda pinion gear. The rack is engaged with the pinion gear disposed at thesecond end of the intermediate shaft 5. Accordingly, when the vehicledriver turns the steering wheel 2, the intermediate shaft 5 and thepinion gear rotate, causing the rack to move horizontally. The rack isfitted with the tie rods 8 at both ends. Accordingly, the tie rods 8move horizontally together with the rack. As a result, since the tierods 8 pull or push the knuckle arms 9, the directions of the steeringtires are changed.

The vehicle is provided with a vehicle speed sensor 11 to detect thevehicle speed V. In the following, the whole of the mechanism whichtransmits the steering force of the steering wheel 2 to the tires 10 maybe referred to as the steering mechanism 100.

In the steering mechanism 100 having the structure described above, whenthe steering wheel 2 is rotated by the vehicle driver, the rotation ofthe steering wheel 2 is transmitted to the steering gear box 7 throughthe steering shaft 3, the torque sensor 4, and the intermediate shaft 5.The rotation of the intermediate shaft 5 is converted into a horizontalmovement of the tie rods 8 within the steering gear box 7. Thehorizontal movement of the tie rods 8 causes the tires 10 to be steered.

The steering wheel-holding state determination section 13 determineswhether the vehicle driver is in a position around the steering wheel 2where the vehicle driver may receive a physical shock due to steering ofthe vehicle. In this embodiment, a pressure sensor is fitted to thesteering wheel 2 to detect whether the vehicle driver is holding thesteering wheel 2. The steering wheel-holding state determination section13 determines whether the vehicle driver is around the steering wheel 2based on the output of the pressure sensor.

Instead of the pressure sensor, there may be provided a camera or aninfrared sensor for detecting whether the vehicle driver is touching thesteering wheel 2 or inserting a hand inside the steering wheel 2, or atorque sensor for detecting the torque applied to the steering wheel 2by the vehicle driver.

The travel direction determination section 16, which operates onelectric power supplied from a vehicle battery (not shown), detects atravelling lane and the position of the vehicle in the travelling lanefrom images imaged by a vehicle-mounted camera (not shown) and sets atarget course based on the detection results. Further, the traveldirection determination section 16 sets a controlled variable used forthe vehicle to run along the target course.

In this embodiment, a target angle θ* which is a target value of thesteering angle (or the motor rotation angle) is set as the controlledvariable, and is outputted to the EPS-ECU 15. Since setting such atarget angle in lane keep control is well known, detailed explanationthereof is omitted here.

The EPS-ECU 15, which operates on electric power supplied from thevehicle battery, calculates a definitive command DC based on the targetangle θ* determined by the travel direction determination section 16,the steering torque detected by the torque sensor 4, the motor rotationangle θ, motor rotation angular velocity ω and motor rotation angularacceleration α which are sent from the motor 6, and the vehicle speed Vdetected by the vehicle speed sensor 11.

The definitive command DC is the sum of an assist command AC which is anelectric current command value to generate the assist torque, thetracking control command TC which is an electric current command valueto generate an automatic steering torque, and an compensation command CCwhich is an electric current command value to suppress vibration. Inthis embodiment, the compensation command CC includes a component forrestricting the driving of the steering wheel 2 to reduce a shockapplied to the vehicle driver when the steering wheel 2 is driven torotate. By applying a drive voltage Vd in accordance with the definitivecommand DC to the motor 6, the assist torque and the automatic steeringtorque are generated.

That is, the EPS-ECU 15 controls the steering characteristics bycontrolling the motor 6 using the driver voltage Vd to thereby controlthe steering mechanism 100 which is driven by the motor 6.

The brake ECU 18 has a function as an electronic control unit forcontrolling braking of the vehicle. The brake ECU 18 complements therestricted steering force of the steering wheel 2 using a brake actuator(not shown) which functions as a driving section other than alater-explained target tracking control arithmetic section 30.

This is because, when the EPS-ECU 15 restricts the steering force byreducing the calculated controlled variable to enable the vehicle totravel along a target course for the purpose of reducing a shock appliedto the vehicle driver, there is a risk that the vehicle cannot travelalong the target course due to inadequacy of the steering force. Hence,the brake ECU 18 controls so as to compensate for shortage of thesteering force by causing only some of the wheels to be applied with abraking force when the EPS-ECU 15 restricts the steering force.

FIG. 2 is a block diagram showing the overall structurer of the EPS-ECU15. As shown in FIG. 2, the EPS-ECU 15 includes an assist controlarithmetic section 20, the target tracking control arithmetic section30, a vibration suppression control arithmetic section 40, an adder 50,a subtractor 55 and a motor driver circuit 60. The assist controlarithmetic section 20 generates the assist command AC.

The target tracking control arithmetic section 30 generates the trackingcommand TC. The vibration suppression control arithmetic section 40generates the compensation command CC. The subtractor 55 generates acompensated version of the tracking command TC by subtracting thecompensation command CC from the tracking command TC. The addergenerates, as a drive command DC, an electric current command value fordriving the motor 6 by adding the assist command AC to the compensatedversion of the tracking command TC.

The motor drive circuit 60 drives the motor 6 by applying the drivevoltage Vd (which is a three-phase voltage when the motor 6 is athree-phase motor) to the motor 6 in accordance with the drive commandDC. The functions of the assist control arithmetic section 20, thetarget tracking control arithmetic section 30, the vibration suppressioncontrol arithmetic section 40, the adder 50 and the subtractor 55 may beimplemented by control programs executed by a CPU (not shown) includedin the EPS-ECU 15.

In this case, the control programs are executed at a given period toensure a necessary responsiveness of the target tracking control (lanekeeping control). The period may be set in a range between severalhundreds of μs and several hundreds of ms.

The EPS-ECU 15 is configured to update the drive command DC at thisperiod. Alternatively, at least part of these functions may beimplemented by a hardware device such as a logic circuit.

The motor drive circuit 60 applies the drive voltage Vd to the motor 6in accordance with the drive command DC so that the assist torque andthe automatic steering torque corresponding to the drive command DC areapplied to the steering shaft. Specifically, the steering shaft iscaused to generate a desired torque by feedback-controlling the drivevoltage Vd such that a current Im flowing through the motor 6 becomesequal to a target current. Since the structure of such a motor drivecircuit is well known (refer to Japanese Patent Application laid-openNo. 2013-52793, for example), detailed explanation is omitted here.

The assist control arithmetic section 20 generates the assist command ACbased on the steering torque Ts, the motor rotation angular velocity ω,and the vehicle speed V. The assist command AC is a torque to assistoperation of the steering wheel 2 so as to realize a feel reflecting theroad surface reaction force and the steering state.

Specifically, the assist control arithmetic section 20 calculates a baseassist amount to obtain a feeling of torque transmission in accordancewith the road surface reaction force based on the steering torque Ts andthe vehicle speed V, calculates an assist compensation amount inaccordance with the steering state depending on the steering torque Tsand the motor rotation angular velocity ω, and generates the assistcommand AC by multiplying the assist compensation amount with a gaindepending on the vehicle speed V. The procedure of calculating theassist command AC is not limited to the one described above, and anyother known procedure may be used.

The target tracking control arithmetic section 30 generates the trackingcommand TC based on the target angle θ*, the steering angle (or motorrotation angle) θ. The steering angle θ may be referred to as the actualangle θ hereinafter. The tracking command TC is an electric currentcommand value for generating the automatic steering torque necessary tocause the actual angle θ to follow the target angle θ*.

In this embodiment, the target tracking control arithmetic section 30obtains a deviation Δθ (=θ*−θ) between the actual angle θ and the targetangle θ*, and defines a control characteristic by imparting a PID gainto this deviation Δθ. The target tracking control arithmetic section 30outputs the tracking command TC depending on the control characteristic.

The tracking command TC is set such that the responsiveness of thetarget tracking control increases with the increase of the PID gain anddecreases with the decreases of the PID gain. The vibration suppressioncontrol arithmetic section 40 calculates a controlled variable used forsuppressing a steering vibration due to steering mechanism oscillationof the steering mechanism 100, and outputs it as the compensationcommand CC. More specifically, in this embodiment, a motion equation isobtained from a model of the steering mechanism as shown in FIG. 3, anda damping control amount is set based on this motion equation.

The motion equation is given as follows.

$\begin{matrix}\left\{ \begin{matrix}{{{J_{1}s^{2}\theta_{1}} + {C_{2}s\; \theta_{1}} + {K_{1}\left( {\theta_{1} - \theta_{2}} \right)}} = 0} \\{{{J_{2}s^{2}\theta_{2}} + {C_{2}s\; \theta_{2}} + {K_{2}\theta_{2}} - {K_{1}\left( {\theta_{1} - \theta_{2}} \right)}} = T_{a}} \\{{K_{1}\left( {\theta_{1} - \theta_{2}} \right)} = T_{s}}\end{matrix} \right. & {{Equation}\mspace{14mu} (1)}\end{matrix}$

-   -   The transfer function based on this motion equation is given by        the following Equation (2).

$\begin{matrix}{\mspace{20mu} {{\theta_{1} = {{\frac{K_{1}}{{J_{1}s^{2}} + {C_{1}\; s} + K_{1}}\theta_{2}} = {\frac{K_{1}}{A}\theta_{2}}}}\mspace{20mu} {A = {{J_{1}s^{2}} + {C_{1}s} + K_{1}}}{T_{a} = {{{\left( {{J_{2}s^{2}} + {C_{2}s} + K_{1} + K_{2}} \right)\theta_{2}} - {\frac{K_{1}}{A}\theta_{2}}} = {\left( {B - \frac{K_{1}}{A}} \right)\theta_{2}}}}\mspace{20mu} {B = {{J_{2}s^{2}} + {C_{2}s} + K_{1} + K_{2}}}\mspace{20mu} {\frac{\theta_{2}}{T_{a}} = \frac{A}{{AB} - K_{1}^{2}}}}} & {{Equation}\mspace{14mu} (2)}\end{matrix}$

When the damping control amount is D, the whole of the control system ofthe EPS-ECU 15 can be shown by the block diagram of FIG. 4. Theinput-output relationship of this control system is given by thefollowing Equation (3).

$\begin{matrix}{\mspace{20mu} {{T_{s} = {{K_{1}\left( {\theta_{1} - \theta_{2}} \right)} = {{K_{1}\left( {{\frac{K_{1}}{A}\theta_{2}} - \theta_{2}} \right)} = {\frac{K_{1}^{2} - A}{A}\theta_{2}}}}}\mspace{20mu} {\theta_{2} = {\frac{A}{{AB} - K_{1}^{2}}\left( {T_{r} - {\frac{K_{1}^{2} - A}{A}D\; \theta_{2}}} \right)}}{\frac{\theta_{2}}{T_{r}} = {\frac{\frac{A}{{AB} - K_{1}^{2}}}{1 + {\frac{A}{{AB} - K_{1}^{2}}\frac{K_{1}^{2} - A}{A}D}} = {\frac{\frac{A}{{AB} - K_{1}^{2}}}{1 + {\frac{K_{1}^{2} - A}{{AB} - K_{1}^{2}}D}} = {\frac{A}{{AB} - K_{1}^{2} + {\left( {K_{1}^{2} - A} \right)D}} = \frac{A}{{A\left( {B - D} \right)} - K_{1}^{2} + {K_{1}^{2}D}}}}}}}} & {{Equation}\mspace{14mu} (3)}\end{matrix}$

By appropriately setting the value of the term (K₁ ²−A)D/A in FIG. 4,vibration of the steering wheel 2 can be suppressed. The value of θ₂/Trin equation (3) is set smaller while the steering wheel-holding statedetermination section 13 detects a presence of the body of the vehicledriver around the steering wheel 2 than while it does not. By thissetting, suppression control to prevent the steering wheel 2 from beingdriven to turn rapidly can be implemented.

In this embodiment, the value of D is set larger while the steeringwheel-holding state determination section 13 detects a presence of thebody of the vehicle driver around the steering wheel 2 than while itdoes not. As a result, as shown in FIG. 5, the amount of change of thesteering angle becomes smaller when the suppression control is performed(see the broken line) than when the suppression control is not performed(see the solid line).

When the EPS-ECU 15 performs the suppression control to suppress thedriving of the steering wheel 2, the EPS-ECU 15 sends a command showingthe content of the suppression control to the notification section 19.In response to this command, the notification section 19 notifies thevehicle driver of the content of the suppression control.

For example, when the suppression control operates to suppress turningof the steering wheel 2, the notification section 19 emits a warningsound, and displays a picture as shown in FIG. 6A near the meter panelof the vehicle. On the other hand, when the suppression control causesthe brake ECU 18 to operate, the notification section 19 displays apicture as shown in FIG. 6B.

The electric steering system 1 described above provides the followingadvantages.

In the electric steering system 1, the target tracking controlarithmetic section 30 drives the steering wheel 2 in accordance with thetarget value. The steering wheel-holding state determination section 13detects a presence of the body of the vehicle driver around the steeringwheel 2. The target tracking control arithmetic section 30 and thevibration suppression control arithmetic section 40 restrict the drivingof the steering wheel 2 by the target tracking control arithmeticsection 30 to reduce a physical shock applied to the vehicle driver fromthe steering wheel 2 depending on the position of the body of thevehicle driver.

According to the electric steering system 1, since the driving of thesteering wheel 2 is restricted depending on the position of the body ofthe vehicle driver, it is possible to reduce a physical shock which thesteering wheel 2 applies to the vehicle driver so that the steeringwheel 2 can be driven safely for the vehicle driver.

In the electric steering system 1, the brake ECU 18 complements therestricted steering force of the steering wheel 2 using the drivesection other than the target tracking control arithmetic section 30.

According to the electric steering system. 1, since the brake ECU 18complements the restricted steering force by causing the drive sectionother than the target tracking control arithmetic section 30 to operate,it is possible to control the behavior of the vehicle satisfactory evenwhen the operation of the target tracking control arithmetic section 30is restricted.

In the electric steering system 1, the target tracking controlarithmetic section 30 and the vibration suppression control arithmeticsection 40 restrict the driving of the steering wheel 2 by the targettracking control arithmetic section 30 by imparting a damping torque tothe output of the target tracking control arithmetic section 30.

According to the electrical steering system 1, it is possible to reducea shock applied to the vehicle driver without modifying the structure ofthe target tracking control arithmetic section 30.

In the electric steering system 1, the steering wheel-holding statedetermination section 13 detects whether the vehicle driver is holdingthe steering wheel 2.

The electric steering system 1 can restrict the driving of the steeringwheel 2 while the steering wheel 2 is detected to be held by the vehicledriver.

In the electric steering system 1, the notification section 19 informsthe vehicle driver of the states of the target tracking controlarithmetic section 30 and the vibration suppression control arithmeticsection 40. According to the electric steering system 1, the vehicledriver can perform a driving operation appropriately taking into accountthe states of the target tracking control arithmetic section 30 and thevibration suppression control arithmetic section 40.

In the electric steering system 1, the target tracking controlarithmetic section 30 drives the steering wheel 2 such that the measuredvalue (the actual steering angle θ) approaches the target value (thetarget angle θ*), and the vibration suppression control arithmeticsection 40 suppress the measured value from approaching the target valuewhile the driving of the steering wheel 2 is restricted.

Therefore, since the turning speed of the steering wheel 2 is suppressedwhile the driving of the steering wheel 2 is restricted, it is possibleto drive the vehicle safely.

Second Embodiment

Next, a second embodiment of the invention is described with a focus ondifferences with the first embodiment.

In the first embodiment described above, the driving of the steeringwheel 2 is restricted using the compensation command CC outputted fromthe vibration suppression control arithmetic section 40. Whereas, in thesecond embodiment, the driving of the steering wheel 2 is restrictedusing the tracking command TC outputted from the target tracking controlarithmetic section 30. More precisely, in the second embodiment, insteadof the target tracking control arithmetic section 30, a target trackingcontrol arithmetic section 30A having the structure shown in FIG. 7 isused.

The target tracking control arithmetic section 30A includes a limiter31A, a subtractor 32A and a PID controller 33A. The limiter 31A has afilter function of restricting the target angle θ*. Specifically, thelimiter 31A restricts the upper limit of the target angle θ*, orrestricts the rate of change of the target angle θ*.

The subtractor 32A outputs the deviation between the output of thelimiter 31A and the actual steering angle θ.

The PID controller 33A generates the PID gain. That is, the PIDcontroller 33A generates a gain for reducing the output of thesubtractor 32A, and outputs it as the tracking command TC.

The limiter 31A is used only while the steering wheel-holding statedetermination section 13 detects a presence of the body of the vehicledriver around the steering wheel 2. In this embodiment, the output ofthe limiter 31A is set valid while the steering wheel-holding statedetermination section 13 detects a presence of the body of the vehicledriver around the steering wheel 2, and otherwise set invalid.

Alternatively, the second embodiment may include both the targettracking control arithmetic section 30 and the target tracking controlarithmetic section 30A. In this case, the output of the target trackingcontrol arithmetic section 30A is used while the steering wheel-holdingstate determination section 13 detects a presence of the body of thevehicle driver around the steering wheel 2, and the output of the targettracking control arithmetic section 30 is used while the steeringwheel-holding state determination section 13 detects no presence of thebody of the vehicle driver around the steering wheel 2.

The second embodiment described above provides the following advantages.The target tracking control arithmetic section 30 suppresses themeasured value from approaching the target value to restrict the drivingof the steering wheel 2 by restricting the range of the target value orby restricting the rate of change or acceleration of change of thetarget value.

Therefore, according to the second embodiment, it is possible to setsuch that the steering wheel 2 is allowed to be driven only within arange in which a shock applied to the vehicle driver is sufficientlysmall.

For example, in the configuration where the limiter 31A restricts therate of change the target angle θ* while the steering wheel-holdingstate determination section 13 detects a presence of the body of thevehicle driver around the steering wheel 2, the rate of change of thesteering angle θ is gentle as shown by the broken line in FIG. 8Acompared to that shown by the solid line in FIG. 8A in the case wherethe limiter 31A is not provided. According to this configuration of thesecond embodiment, since the rate of change of the steering angle isrestricted when the steering wheel 2 is turned to a target position, ashock applied to the vehicle driver can be reduced.

In another configuration where the limiter 31A restricts the upper limitof the target angle θ*, the amount of change of the steering angle θ islimited (see the broken line in FIG. 8B) compared to that in the casewhere the limiter 31A is not provided (see the solid line in FIG. 8B).According to this configuration of the second embodiment, although therate of change of the steering angle is not restricted, it is possibleto reduce a shock applied to the vehicle driver by setting the upperlimit of the target angle θ* depending on the detected position of thebody of the vehicle driver such that the steering wheel 2 does not touchthe vehicle driver.

Other Embodiments

The components of the electric steering systems according to the abovedescribed embodiments may be implemented by executing computer programsstored in a storage device.

Instead of the target tracking control arithmetic section 30, a targettracking control arithmetic section 30B having the structure shown inFIG. 9 may be used to restrict the driving of the steering wheel 2. Asshown in FIG. 9, the target tracking control arithmetic section 30Bincludes a limiter 30B, a subtractor 32B and a PID controller 33B.

The subtractor 32B outputs a signal indicating the deviation between thetarget steering angle θ* and the actual steering angle θ. The limiter31B restricts the upper limit or the rate of change of the output of thesubtractor 32B. The limiter 31B is used only when the steeringwheel-holding state determination section 13 is detecting a presence ofthe body of the vehicle driver around the steering wheel 2.

That is, the target tracking control arithmetic section 30B suppressesthe measured value from approaching the target value by changing themagnitude of the signal indicating the deviation between the targetvalue and the actual value to a smaller value, or by changing the rateof change or acceleration of change of the target value to a smallervalue.

Also by using the target tracking control arithmetic section 30B, it ispossible to prevent the steering wheel 2 from being driven to rotaterapidly, to reduce a shock applied to the vehicle driver. The solidlines of FIG. 10A and FIG. 10B show examples of the rate of change ofthe steering angle θ when the limiter 30B is not used, while the brokenlines of FIG. 10A and FIG. 10B show examples of the rate of change ofthe steering angle θ when the limiter 30B is used.

Further, instead of the target tracking control arithmetic section 30, atarget tracking control arithmetic section 30C having the structureshown in FIG. 11 may be used. The target tracking control arithmeticsection 30C includes a subtractor 32C and a PID controller 33C. Thetarget tracking control arithmetic section 30C does not include alimiter.

The PID controller 33C, which imparts a PID gain to the output of thesubtractor 32C, can vary the PID gain in accordance with the output ofthe steering wheel-holding state determination section 13. Specifically,the PID gain is set smaller while the steering wheel-holding statedetermination section 13 detects a presence of the body of the vehicledriver around the steering wheel 2 than while it does not.

That is, the target tracking control arithmetic section 30 reduces theresponsiveness in causing the measured value to approach the targetvalue to restrict the driving of the steering wheel 2. This makes itpossible to suppress the steering wheel 2 from being driven rapidly, toreduce a shock applied to the vehicle driver.

Instead of the target tracking control arithmetic section 30, a targettracking control arithmetic section 30D having the structure shown inFIG. 12 may be used. The target tracking control arithmetic section 30Dincludes a limiter 31D, a subtractor 32D and a PID controller 33D.

The subtractor 32D outputs a signal indicating the deviation between thetarget steering angle θ* and the actual steering angle θ. The PIDcontroller 33D imparts a PID gain to the output of the subtractor 32D.The limiter 31D restricts the upper limit or the rate of change of theoutput of the PID controller 33D. The limiter 31D is used only while thesteering wheel-holding state determination section 13 detects a presenceof the body of the vehicle driver around the steering wheel 2.

The target tracking control arithmetic section 30 suppresses themeasured value from approaching the target value by restricting thecontrolled variable to restrict the driving of the steering wheel 2.

This makes it possible to suppress the steering wheel 2 from beingdriven urgently to reduce a shock applied to the vehicle driver. Thesolid line of FIG. 13 shows an example of the rate of change of thesteering angle θ when the limiter 31D is not provided, while the brokenline of FIG. 13 shows an example of the rate of change of the steeringangle θ when the limiter 31D is used.

In the first embodiment, the damping using the steering torque Ts isimplemented by the vibration suppression control arithmetic section 40.However, it may be implemented using the motor rotation angular velocityco. In this case, a motion equation is obtained from a model of thesteering mechanism as shown in FIG. 14, and a damping amount is setbased on the motion equation.

The motion equation is given as follows.

T _(a) =Js ² θ+Csθ+Kθ=(Js ² +Cs+K)θ  Equation (4):

-   -   The transfer function based on this motion equation is given by        the following Equation (5).

$\begin{matrix}{\frac{\theta}{T_{a}} = \frac{1}{{Js}^{2} + {Cs} + K}} & {{Equation}\mspace{14mu} (5)}\end{matrix}$

When the damping control amount is D, the whole of the control system ofthe EPS-ECU 15 can be shown by the block diagram of FIG. 15. Theinput-output relationship of this control system is given by thefollowing Equation (6).

$\begin{matrix}{{\theta = {\frac{1}{{Js}^{2} + {Cs} + K}\left( {T_{r} - {{Ds}\; \theta}} \right)}}{\frac{\theta}{T_{r}} = {\frac{\frac{1}{{Js}^{2} + {Cs} + K}}{1 + {\frac{1}{{Js}^{2} + {Cs} + K^{2}}{Ds}}} = \frac{1}{{Js}^{2} + {\left( {C + D} \right)s} + K}}}} & {{Equation}\mspace{14mu} (6)}\end{matrix}$

If the above equation is set such that the damping amount D is largerwhile the steering wheel-holding state determination section 13 detectsa presence of the body of the vehicle driver around the steering wheel 2than while it does not, it is possible to suppress the steering wheelfrom being driven rapidly to reduce a shock applied to the vehicledriver. As a result, as shown in FIG. 16, the amount of the steeringangle is smaller when the suppression control is performed (see thebroken line) than when the suppression control is not performed (see thesolid line).

The damping may be implemented using the rate of temporal change of thesteering torque Ts. In this case, a motion equation similar to equation(1) is obtained from the model of the steering mechanism as shown inFIG. 3, and the damping amount D is set based on the motion equation.

The transfer function based on this motion equation is given by thefollowing Equation (7).

$\begin{matrix}{{\frac{\theta_{2}}{T_{a\;}} = \frac{A}{{AB} - K_{1}^{2}}}{T_{s} = {{K_{1}\left( {\theta_{1} - \theta_{2}} \right)} = {\frac{K_{1}^{2} - A}{A}\theta_{2}}}}} & {{Equation}\mspace{14mu} (7)}\end{matrix}$

When the damping control amount is D, the whole of the control system ofthe EPS-ECU 15 can be shown by the block diagram of FIG. 17. Theinput-output relationship of this control system is given by thefollowing Equation (8).

$\begin{matrix}\begin{matrix}{\frac{\theta_{2}}{T_{r}} = \frac{\frac{A}{{AB} - K_{1}^{2}}}{1 + {\frac{A}{{AB} - K_{1}^{2}}\frac{K_{1}^{2} - A}{A}{Ds}}}} \\{= \frac{\frac{A}{{AB} - K_{1}^{2}}}{1 + {\frac{K_{1}^{2} - A}{{AB} - K_{1}^{2}}{Ds}}}} \\{= \frac{A}{{AB} - K_{1}^{2} + {\left( {K_{1}^{2} - A} \right){Ds}}}} \\{= \frac{A}{{A\left( {B - {Ds}} \right)} - K_{1}^{2} + {K_{1}^{2}{Ds}}}}\end{matrix} & {{Equation}\mspace{14mu} (8)}\end{matrix}$

If the above equation is set such that the damping amount D is largerwhile the steering wheel-holding state determination section 13 detectsa presence of the body of the vehicle driver around the steering wheel 2than while it does not detect, it is possible to suppress the steeringwheel 2 from being driven rapidly to reduce a shock applied to thevehicle driver. As a result, as shown in FIG. 18, the rate of change ofthe steering angle is smaller when the suppression control is performed(see the broken line) than when the suppression control is not performed(see the solid line).

The damping may be implemented using the road load Ti between the roadsurface and the tires of the vehicle. In this case, a motion equationsimilar to equation (1) is obtained from a model of the steeringmechanism as shown in FIG. 3, and the damping amount is set based onthis motion equation.

The transfer function based on this motion equation is given by thefollowing Equation (9).

$\begin{matrix}{{\frac{\theta_{2}}{T_{a}} = \frac{A}{{AB} - K_{1}^{2}}}{T_{s} = {{K_{1}\left( {\theta_{1} - \theta_{2}} \right)} = {\frac{K_{1}^{2} - A}{A}\theta_{2}}}}{T_{i} = {{T_{a} + T_{s}} = {T_{a} + {\frac{K_{1}^{2} - A}{A}\theta_{2}}}}}} & {{Equation}\mspace{14mu} (9)}\end{matrix}$

When the damping control amount is D, the whole of the control system ofthe EPS-ECU 15 can be shown by the block diagram of FIG. 19. Theinput-output relationship of this control system is given by thefollowing Equation (10).

$\begin{matrix}{{T_{a} = {T_{r} - {D\left( {T_{a} + {\frac{K_{1}^{2} - A}{A}\theta_{2}}} \right)}}}{{\left( {1 + D} \right)T_{a}} = {T_{r} - {D\; \frac{K_{1}^{2} - A}{A}\theta_{2}}}}{T_{a} = {{\frac{1}{1 + D}T_{r}} - {\frac{D}{1 + D}\frac{K_{1}^{2} - A}{A}\theta_{2}}}}\begin{matrix}{\theta_{2} = {\frac{A}{{AB} - K_{1}^{2}}T_{a}}} \\{= {\frac{A}{{AB} - K_{1}^{2}}\left\{ {{\frac{1}{1 + D}T_{r}} - {\frac{D}{1 + D}\frac{K_{1}^{2} - A}{A}\theta_{2}}} \right\}}} \\{= {{\frac{A}{{AB} - K_{1}^{2}}\frac{1}{1 + D}T_{r}} - {\frac{A}{{AB} - K_{1}^{2}}\frac{D}{1 + D}\frac{K_{1}^{2} - A}{A}\theta_{2}}}}\end{matrix}} & {{Equation}\mspace{14mu} (10)} \\{{\left( {1 + \frac{\left( {K_{1}^{2} - A} \right)D}{\left( {{AB} - K_{1}^{2}} \right)\left( {1 + D} \right)}} \right)\theta_{2}} = {\frac{A}{\left( {{AB} - K_{1}^{2}} \right)\left( {1 + D} \right)}T_{r}\begin{matrix}{\frac{\theta_{2}}{T_{r}} = \frac{A}{{\left( {{AB} - K_{1}^{2}} \right)\left( {1 + D} \right)} + {\left( {K_{1}^{2} - A} \right)D}}} \\{= \frac{A}{{AB} + {ABD} - K_{1}^{2} - {K_{1}^{2}D} + {K_{1}^{2}D} - {AD}}} \\{= \frac{A}{{A\left\{ {{\left( {1 + D} \right)B} - D} \right\}} - K_{1}^{2}}}\end{matrix}}} & \;\end{matrix}$

If the above equation is set such that the damping amount D is largerwhile the steering wheel-holding state determination section 13 detectsa presence of the body of the vehicle driver around the steering wheel 2than while it does not detect the driver, it is possible to suppress thesteering wheel 2 from being driven rapidly to reduce a shock applied tothe vehicle driver. As a result, as shown in FIG. 20, the amount or therate of change of the steering angle is smaller when the suppressioncontrol is performed (see the broken line) than when the suppressioncontrol is not performed (see the solid line).

The damping may be implemented using the rate of change of the road loadTi. In this case, a motion equation similar to equation (1) is obtainedfrom a model of the steering mechanism as shown in FIG. 3, and thedamping amount is set based on this motion equation.

The transfer function based of this motion equation is given by thefollowing Equation (11).

$\begin{matrix}{{\frac{\theta_{2}}{T_{a}} = \frac{A}{{AB} - K_{1}^{2}}}{T_{s} = {{K_{1}\left( {\theta_{1} - \theta_{2}} \right)} = {\frac{K_{1}^{2} - A}{A}\theta_{2}}}}{T_{i} = {{T_{a} + T_{s}} = {T_{a} + {\frac{K_{1}^{2} - A}{A}\theta_{2}}}}}} & {{Equation}\mspace{14mu} (11)}\end{matrix}$

When the damping control amount is D, the whole of the control system ofthe EPS-ECU 15 can be shown by the block diagram of FIG. 21. Theinput-output relationship of this control system is given by thefollowing Equation (12).

$\begin{matrix}{\mspace{20mu} {{T_{a} = {T_{r} - {{Ds}\left( {T_{a} + {\frac{K_{1}^{2} - A}{A}\theta_{2}}} \right)}}}\mspace{20mu} {{\left( {1 + {Ds}} \right)T_{a}} = {T_{r} - {{Ds}\; \frac{K_{1}^{2} - A}{A}\theta_{2}}}}\mspace{20mu} {T_{a} = {{\frac{1}{1 + {Ds}}T_{r}} - {\frac{Ds}{1 + {Ds}}\frac{K_{1}^{2} - A}{A}\theta_{2}}}}\begin{matrix}{\theta_{2} = {\frac{A}{{AB} - K_{1}^{2}}{Ta}}} \\{= {\frac{A}{{AB} - K_{1}^{2}}\left\{ {{\frac{1}{1 + {Ds}}T_{r}} - {\frac{Ds}{1 + {Ds}}\frac{K_{1}^{2} - A}{A}\theta_{2}}} \right\}}} \\{= {{\frac{A}{{AB} - K_{1}^{2}}\frac{1}{1 + {Ds}}T_{r}} - {\frac{A}{{AB} - K_{1}^{2}}\frac{Ds}{1 + {Ds}}\frac{K_{1}^{2} - A}{A}\theta_{2}}}}\end{matrix}}} & {{Equation}\mspace{14mu} (12)} \\{{{\left( {1 + \frac{\left( {K_{1}^{2} - A} \right){Ds}}{\left( {{AB} - K_{1}^{2}} \right)\left( {1 + {Ds}} \right)}} \right)\theta_{2}} = {\frac{A}{\left( {{AB} - K_{1}^{2}} \right)\left( {1 + {Ds}} \right)}T_{r}}}\begin{matrix}{\mspace{20mu} {\frac{\theta_{2}}{T_{r}} = \frac{A}{{\left( {{AB} - K_{1}^{2}} \right)\left( {1 + {Ds}} \right)} + {\left( {K_{1}^{2} - A} \right){Ds}}}}} \\{= \frac{A}{{AB} + {ABDs} - K_{1}^{2} - {K_{1}^{2}{Ds}} + {K_{1}^{2}{Ds}} - {ADs}}} \\{= \frac{A}{{A\left\{ {{\left( {1 + {Ds}} \right)B} - {Ds}} \right\}} - K_{1}^{2}}}\end{matrix}} & \;\end{matrix}$

If the above equation is set such that the damping amount D is largerwhile the steering wheel-holding state determination section 13 detectsa presence of the body of the vehicle driver around the steering wheel 2than while it does not, it is possible to suppress the steering wheel 2from being driven rapidly, to reduce a shock applied to the vehicledriver. As a result, as shown in FIG. 22, the amount or the rate of thesteering angle is smaller when the suppression control is performed (seethe broken line) than when the suppression control is not performed (seethe solid line).

The electric steering systems according to the above describedembodiments may be provided with an arbitration section 17 having thestructure shown FIG. 23. The arbitration section 17 is disposed on thesignal line between the travel direction determination section 16 andthe EPS-ECU 15, for example. The arbitration section 17 restricts thedriving of the steering wheel 2 when there is an abnormality in thesteering wheel-holding state determination section 13. The arbitrationsection 17 determines that there is an abnormality in the steeringwheel-holding state determination section 13 if the signal received fromthe steering wheel-holding state determination section 13 does notchange for over a predetermined time, or if no signal is received fromthe steering wheel-holding state determination section 13. In this case,the arbitration section 17 restricts the upper limit or the rate ofchange of the target steering angle θ*.

The provision of the arbitration section 17 makes it possible to drivethe steering wheel 2 safely even when there is an abnormality in thesteering wheel-holding state determination section 13. The electricsteering systems according to the above described embodiments may beconfigured to provide various information depending on the state ofdetection by the steering wheel-holding state determination section 13or the state of restriction of the driving of the steering wheel 2. Forexample, the degree of the holding force applied to the steering wheel 2by the vehicle driver may be displayed as pictures as shown in FIGS. 24Aand 24B.

When the steering wheel 2 is not held by the vehicle driver, a pictureto encourage the vehicle driver to hold the steering wheel 2 as shown inFIG. 15 may be displayed. When an abnormality is detected in thesteering wheel-holding state determination section 13, a picture toinform the vehicle driver of the malfunction as shown in FIG. 25B may bedisplayed.

These pictures may be displayed reflecting a positional relationshipbetween the steering wheel 2 and a part (palms or arms, for example) ofthe body of the vehicle driver detected by the steering wheel-holdingstate determination section 13. In this case, the vehicle driver canconfirm whether the detection result of the sensor agrees to thebehavior of the vehicle driver.

The reduction gear device 6 a may be configured such that its gear ratiois variable depending on the vehicle state such as the vehicle speed.That is, the above described embodiments may include a variable gearratio steering actuator. In this case, the target tracking controlarithmetic section 30 or the vibration suppression control arithmeticsection 40 may command the variable gear ratio steering actuator to setthe target gear ratio such that the steering drive speed is reduced whenthe driving of the steering wheel 2 is restricted.

More specifically, the electric steering system may be configured asshown in FIG. 26. This configuration includes a VGRS (Variable GearRatio Steering) 80 and a VGRS-ECU 70.

The VGRS-ECU 70 sets the amount of change of the tire steering anglerelative to the steering amount (that is, the gear ratio) in accordancewith the vehicle speed V and the target steering angle θ*, and outputthis setting to the VGRS 80. As shown in FIG. 26, the VGRS-ECU 70includes a CPU and a memory (not shown). This CPU provides the functionsof a target relative angle calculation arithmetic section 71, a steeringwheel rotation suppression arithmetic section 72, an adder 73 and amotor drive circuit 74.

The target relative angle calculation arithmetic section 71 calculates atarget relative angle between the steering wheel and the pinion anglebased on the vehicle speed V and the target steering angle θ*. Thesteering wheel rotation suppression arithmetic section 72 calculates acontrolled variable (gear ratio) to suppress the rotation of thesteering wheel.

The adder 73 sums the output of the target relative angle calculationarithmetic section 71 and the output of the steering wheel rotationsuppression arithmetic section 72, and sends the result of the summationto the motor drive circuit 74. The motor drive circuit 74 generates acommand value to set the gear ratio in accordance with the result of thesummation, and outputs it to the VGRS 80. The output of the motor drivecircuit 74 enables driving a not-shown motor within the VGRS 80 so as toachieve the target relative angle while suppressing the steering wheelfrom being driven to rotate.

The VGRS 80 drives the motor therein to set the gear ratio in accordancewith the command value to set the gear ratio. The electric steeringsystem having such a configuration can reduce a shock applied to thevehicle driver, because the variable gear ratio steering actuator setsthe target gear ratio such that the steering drive speed is reduced whenthe driving of the steering wheel 2 is restricted.

In the above embodiments, the brake actuator complements the steeringforce when the driving of the steering wheel 2 is restricted. However,an actuator having the function of DRS (Dynamic Rear Steering) or anactuator that performs engine control or motor control may be usedinstead of the brake actuator.

Correspondence between the embodiments described above and the appendedclaims:

The electric steering system corresponds to the steering wheel controlapparatus. The steering wheel-holding state determination section 13corresponds to the body position detection section. The target trackingcontrol arithmetic section 30 corresponds to the steering wheel drivesection. The target tracking control arithmetic section 30 correspondsto the steering angle driving restriction section. The target trackingcontrol arithmetic section 30, the vibration suppression controlarithmetic section 40 and the arbitration section 17 correspond to thesteering wheel driving restriction section and the abnormality detectionsection. The brake ECU 18 corresponds to the complementary section.

The above explained preferred embodiments are exemplary of the inventionof the present application which is described solely by the claimsappended below. It should be understood that modifications of thepreferred embodiments may be made as would occur to one of skill in theart.

What is claimed is:
 1. A steering wheel control apparatus forcontrolling driving of a steering wheel of a vehicle, comprising: asteering wheel drive section that drives the steering wheel inaccordance with a target value; a shock probability determinationsection that determines whether the steering wheel may apply a shock toa vehicle driver; and a steering wheel driving restriction section thatrestricts driving of the steering wheel by the steering wheel drivesection to reduce the shock applied to the vehicle driver when the shockprobability determination section determines that the steering wheel mayapply the shock to the vehicle driver.
 2. The steering wheel controlapparatus according to claim 1, further comprising a complementarysection that complements a steering force of the steering wheel using adrive section other than the steering wheel drive section when thesteering wheel driving restriction section restricts driving of thesteering wheel.
 3. The steering wheel control apparatus according toclaim 1, wherein the steering wheel drive section drives the steeringwheel such that a measured value related to the steering wheelapproaches the target value, and the steering wheel driving restrictionsection suppresses the measured value from approaching the target valueto restrict driving of the steering wheel.
 4. The steering wheel controlapparatus according to claim 3, wherein the steering wheel drivingrestriction section suppresses the measured value from approaching thetarget value by restricting a set range of the target value, or byrestricting a rate or an acceleration of change of the target value whenthe target value is changed.
 5. The steering wheel control apparatusaccording to claim 3, wherein the steering wheel driving restrictionsection suppresses the measured value from approaching the target valueby changing a value of a deviation between the measured value and theactual value to a smaller value, or by changing the rate or accelerationof change of the target value to a smaller value when the value of thedeviation is changed.
 6. The steering wheel control apparatus accordingto claim 3, wherein the steering wheel driving restriction sectionreduces a responsiveness in causing the measured value to approach thetarget value to restrict driving of the steering wheel.
 7. The steeringwheel control apparatus according to claim 3, wherein the steering wheeldrive section sets a controlled value for causing the measured value toapproach the target value and drives the steering wheel in accordancewith the controlled variable, and the steering wheel driving restrictionsection restricts the controlled variable to suppress the measured valuefrom approaching the target value to restrict driving of the steeringwheel.
 8. The steering wheel control apparatus according to claim 1,wherein the steering wheel driving restriction section imparts a dampingtorque to an output of the steering wheel drive section to restrictdriving of the steering wheel.
 9. The steering wheel control apparatusaccording to claim 1, wherein the steering wheel driving restrictionsection sets a target gear ratio of a variable gear ratio steeringactuator of the vehicle such that a steering wheel drive speed isreduced.
 10. The steering wheel control apparatus according to claim 1,wherein, the shock probability determination section includes a bodyposition detection section that detects a position of a body of thevehicle driver around the steering wheel.
 11. The steering wheel controlapparatus according to claim 1, wherein, the body position detectionsection detects a holding state of the steering wheel by the vehicledriver.
 12. The steering wheel control apparatus according to claim 1,further comprising a notification section that informs the vehicledriver of an operation state of the steering wheel driving restrictionsection.
 13. The steering wheel control apparatus according to claim 1,further comprising an abnormality detection section for detecting anabnormality in the shock probability determination section, the steeringwheel driving restriction section being configured to restrict drivingof the steering wheel when the abnormality detection section detects theabnormality in the shock probability determination section.